Optical biosensing provides an opportunity for the detailed characterization of surface-immobilized molecules with soluble binding partners. Recently, we have introduced a new biophysical framework for the quantitative interpretation of binding data measured by surface plasmon resonance biosensing, considering ensembles of surface sites with a quasi-continuous distribution of affinity and kinetic rate constants for binding with the soluble analyte. An area of major application for this method was the characterization of antibodies against different antigens derived from Japanese encephalitis virus, in collaboration with LID/NIAID. A second application of this method was the study of IgG Fc-receptor interactions, also in collaboration with LID/NIAID.[unreadable] [unreadable] Analytical ultracentrifugation provides unique information on protein self-association and hetero-association in solution. We have previously developed techniques for the computational deconvolution of diffusion to arrive at high-resolution sedimentation coefficient distributions, and have shown theoretically how these can be interpreted quantitatively in the framework of coupled migration and chemical reaction, representing a robust method for measuring macromolecular binding constants. Extending this approach, we have implemented Bayesian strategies to exploit prior knowledge available on the molecules under study. These tools were applied in collaboration with LI/NIAID to the characterization of different cytomegalovirus proteins and their interactions. In collaboration with LCMN/NICHHD, this approach was also used to study the role of self-association of glutamate receptor variants, as well as the homo-and hetero-association of NMDA receptors. Further, we conducted several additional collaborative analytical ultracentrifugation studies with proteins of different IRP laboratories, including ROR alpha (NICHHD), IgM domains (NIAID), ASAP1 (NCI), and others.